Hot extrusion of metals



Oct. 11, 1960 y J. sEJouRNET 2,955,709

Hoz' ExTRUsIoN oF METALS Filed June 10, 1953 "E presses comprisingVessentially a container in which the States Patent tice 1,955,709 -0nor XTRUsIo'oFimTALs i Jacques Sejournet, Paris; France,`a`ssignor toCompagnie du Filage des Metaux et des Joints Curty :"'Fiifi'rii 10,1953, SerINO. 360,708 Claimspriority, application France July'l, 1952 -6claims.' (Cl. 207-10) The "present invention concernsY the hot extrusionof 'metal`s,;Which i's generally effected by means of hydraulic Srnetalbillet'toibe transformedis placed, a die which tits "at on'e end ofthisvcont-ainsiA and the oriiiceof 'which rep- 'resents the cross section ofthe part which it is desired to' obtain by extrusion, and a punch whichenters the containerandpresseson the end'of the billet opposite`thatfacing `'the dieand` `tnansfrnitsto said billet theforce :developedby 'the'. press, so Kas to force the metal Vof the billet through thedie. j

s The great-number of the `metals. and alloys submitted to such a pressextrusion process'doV not in `general pre- 'sentf surfaceifaults. Metalsandalloys, however, of poorly rduictilej nature 'or f'badV homogeneityand 'more particulanly diiiioult to extrude, provide such fault-s after`extrusion." x m One of these faults is constituted vby cnacksglocalizedat thehont end Iof the extruded Iliar,-whicl1 may be circularcracks,`off ktlie'solcalledV palm -"1:reetype, or spreading cracks, thelatter occurring generallyin products. ex-

, 'truded from-cast billets.

Cb=4, Fe=4);'Siliconbronze (copper 97,` silicon 3).

The presence Vof these yfau-ltsrrnakes it necessary to pare olf thefronttendsof theextnded a`rs,"wlich constitutes iafseriouseconomic-disadvantage 'ias inf general the `metals or alloys dealt withare costly. f l j A -"obj"e`c`t 'ofthe-present Iinvention is to providea p'rbcess which makes `-it-possibleto"avoid in alpactically mann the-formation I'the'fa'ult's above referred t'; 'and lto 'decrease 4ina-11important proportion the length of the portion tobe pared olf at thefront ends of the exi 4 truded bars. l

Said 'Aprfdess--consistg essentillyjinplacing, between the billet ofmetal to be extruded and the bottom off the extrusion press container,an auxiliary part, for instance a disc of a simple metal or of an alloydifferent from that constituting the billet and covering substantiallythe entire area of the end of the billet, lthe nature and propl ertiesof the metal forming said part being selected by experience, as beingcapable of preventing the formation of undesirable faults.

The thickness of the metal disc thus placed in front of the billetshould be fairly high, for instance on the order of 5 to 50% of itsdiameter. It may be either secured by any known means, such as welding,for instance, on the front of the billet, before extrusion, orpreviously placed in the bottom of the container.

When extrusion takes place under such conditions, the disc is deformedat the beginning of the extrusion Vand covers the rst portion of theextruded bar, thus preventing the formation of the above mentionedcracks. After extrusion it is then suiiicient to separate said vportionof Patented Oct: l1-1, 1960 the bar, which is rthus covered, and whichis very substantiallysho'rter thanthat on which the cracks would -have'occuied in the case of' a direct extrusion of the billet,.witl`1outinterposing of the disc according to the process of the'piesentinvention. s

The explanationof this result, @as well as more precise detailsas to themanner of carrying out the invention are givenv hereinafter -withreference to the appended drawing wherein:

Figlre lis a-pespective view Vof Vthe end of an extruded "cylindricalbar having so-called palm ltree cracks: j

Figure '2' isiasiinilar view of a bar having spreading or flaringcracks.

Figure 3 is a 'diagrammatic view, showing a billet 1 and a container 6'forthe billet, before the billet has been placed in the container, thebillet being shown as divided into 'imaginary slices' 1a-1e.

Figure 4 is -a` diagrammatic view, showing the billet l partiallyextruded intothe bar 2.V

Figure 5 is a view in diametral section of a billet pro vided with a'disc according to the invention.

' Figure 6 is 'a 'similar view of theV front end Aof'an eX- truded bar,acordingto the invention,` made from the billet offFi'gure 5.

As indicatedfabove,-during the extruding of som inetalswand; alloys.which have poor ductility or which are lackingin homogeneity, there mayoccur, at the front end Athrough thedie'7 into aba'r 2 (Figure 4), theimaginary parallel slices*1;1e'ofth billet 1 are deformed into-slr'apesfZ'a-le which nest linto one another as shown in VFigureY 4.'Thec'eitna'l portion a .(Figure 3) 'ofthe vfruit face ofthe billet,v"corresponding tothe cross section of the `die is punched'by the latterand becomes, after extrusion, a slightly bulging surace A (Figure 4).The remainder bf the front face of the billet, or annular surface by(Figure '3)"c`overs the lirst portion of the extruded bar wat B (Figure21). The/'cylindrical surface c (Figure 3) of the billet becomes, vafterextrusion, the remainder C (Figuref'4) of fthe'extrude'dv bar. TheVsurface a undergoespnactically no 'superficial deformation, the surface'c undergoes ifa practically constant deformation from one to 'the other"end of the billet, and the surface b undergoes very' 'importantincreasing superficial deformation,

YThese 'differences' in deformation and the Vswaging of' the variousslices on one another, entail the'productionfin :the headportionofitheextruded bar, of tensions which, infextrtfding metals :or alloys,fsteels, for instance;'poo1"ly duotile or not suciently homogeneous,cause the formation of the above mentioned faults, and the entireportion of the bar which offers such faults has to be cut-off andrejected.

To prevent the economic icon-sequences of this phenomenon of cracks.,according to the invention a disc 4 is placed in front of the billet 1(Figure 5). This disc is made of a metal or alloy which, duringextrusion, does not cause the formation of said faults, said disc beingattached'to the billet, by welding for instance.

i During extrusion, the disc 4 is subjected to a deformation similar tothat undergone, in the case of Figures 3 and 4, by the slice 1a of thebillet 1 and covers at 4a (Figure 6), the frontend of the bar 5 extrudedfrom the billet 1, preventing the formation of faults. It is thensuicient to cut-off the portion of the bar 5 which is covered by thedefonrned disc 4a, while inthe case of Figure 4, it is often necessaryto reject the whole end of the extruded bar, up to the slice 2e.

-Insteadrof being connected with the billet 1 before extrusion, andtherefore heated to the same temperature as the billet, the disc 4 maybe placed at the bottom of the extrusion press container, beforeintroducing the billet. It is then possible to heat the disc either 5tothe Vsame temperature as the billet, or to a different temperature,which makes it possible if necessary, to adjust the re-l sistance todeformation of the metal constituting the disc to that of the metalconstituting the billet. i

VA metal is generally used, for the disc, offering a lower resistance todeformation than that of the .billet at the same temperature. results ina new advantage, i.e. decreasingthe extrusion pressure at the start, andthere- 'fore increasing thevpossibilities of deformation.

Thus for extruding a high speed steel such as above referred to, acar-bon steel disc may be used, and for extruding silicon bronze, anordinary bronze disc.

Experience has shown that the process according to the Vinvention givesall Vthe better results as the tool lubrication is itself more thoroughin operation. It is therefore recommended to lapply this process witha'suitable lubrication, and more particularly by using as lubricant, aproduct which can melt in Contact with the billet or the tool at theoperation temperature, while remaining viscous, and especially glass.

When the disc 'and billet are at different temperatures, it maybesuitable to adjust the lubricant tothe temperature, therefore to use ajuxtaposition of glasses having substantially the same viscosity, one atthe temperature of the disc land the other o'ne at the temperature ofthe metal to be extruded. The amountsof these two lubricants should, ofcourse, be adjusted to the relative sizes of the two surfaces ofdifferent natures to be lubricated.

The lfollowing examples illustrate various practical embodiments of theprocess of the invention.

Example 1 -T-he extrusion was effected, in a container having a diameterof 140 mm., with a 1500 ton press, on billets of S.816 steel, 130 mm. indiameter and 300 `mm.long, into round bars 35 mm. in diameter.

extruded bars, reaching 0.50 rn.

When on the contrary and according to the invention, a steel disc (0.1canbon) and 30 mm. thick was welded in front of the billet, by operatingunder the same conditions otf .temperature and lubrication, faultlessbars were obtained, a 50 mm. length of which merely was covered by thedeformed disc, as shown in Figure 6. 4The metal of the disc was easilyseparated from that of the bar. Y

Example 2.-In a container 148 mm. in diameter, with a 1500 ton press,billets` of pure'molybdenum, 140 mm. in diameter and 450 mm. long, wereextruded into round bars 80 mm. in diameter.

Proceeding with the extrusion inv the 'usual manner, after raising thebillet to a temperature of 1350 C., and

vlubricating by means of Pyrex glass, the formation of ared cracks wasfound over an extruded length reaching to 0.10 m.

If, on the contrary, a few seconds before introducing the billet, asteel disc (0.1 carbon) was introduced into the container, mm. thick andraised to a temperature of 1100 C. using as a lubricant glass woolplaced between the Pyrex glass and the disc, faultless bars wereobtained on which -a length of a few centimeters only was covered by thedeformed disc.

What I claim is:

1. In a method of extruding a heated solid metal billet through a die toform a solid bar, the steps comprising interposing between the leadingend face of the billet and the die, prior to extrusion, an auxiliarymetal part covering substantially the entire area of said leading endface, the auxiliary metal part and the billet, at the temperatureemployed for each of them, being such that the lauxiliary metal partoffers a lower resistance to deformation than the billet, said auxiliarymetal part being of such thickness that it forms only a short cap on thefront l end of the bar extruded Vfrom the billet, extruding all of lsaidauxiliary metal part land all but a small portion of the billet throughthe die, the billet having such poor ductility at the extrusiontemperature employed that the front end of the extruded bar would crackif said auxiliary metal part were not employed, and severing the frontend portion of the extruded bar covered by said cap from the remainderof said extruded bar.

2'. A method according to claim 1, wherein the metal of the billet ishigh speed steel.

3. A method according to claim 1, wherein the metal of the billet ishigh speed steel and said auxiliary metal part is low carbon steel.

4. A method according to claim 1, wherein the metal of the billet isrefractory steel.

5. A method according to claim 1, wherein the metal of the billet isrefractory steel and said auxiliary metal part is low carbon steel.

v 6. A method according to claim 1, wherein the metal of the billet issilicon bronze and wherein said auxiliary metal part is bronze of acharacter which offers a lower resistance to deformation than thesilicon bronze at the temperatures of the billet and auxiliary metalpart.

